The invention relates generally to weld wires useful in joint and surface welding and more specifically to solid and metal-core weld wires which produce improved weld deposits having self-peeling or readily removable slag islands.
Solid and metal cored weld wires are commonly employed in electric arc welding of mild and low alloy steel base metals. These wires yield high strength welds in a single pass and multiple pass at high welding speed. These weld wires are formulated to provide a solid, nonporous weld bead with tensile strength, ductility and impact strength to meet the desired end use applications. Solid and metal cored wires are also formulated to minimize slag, however, small slag islands or a thin line of slag is often produced in the weld toe. These islands or slag lines must be removed before painting or coating the weld, because if they peel off after the weld is painted or coated, they detract from the appearance of the product or serve as corrosion initiation sites.
Solid wire is one of the most popular types of welding wire. Continuous welding made possible by solid wire leads to higher productivity when compared to shielded metal arc welding (stick electrode welding). Solid wires are made by drawing hot rolled rod of a specific chemistry to a desired diameter. Solid wire is then cleaned and copper plated if necessary. Manganese and silicon present in the solid wire oxidizes during the welding process and produces isolated, thin slag islands. The productivity advantages which solid wires provide are sometimes offset by the time required to remove the slag deposits or islands that form on the surface of the weld.
Metal-core wires are used increasingly as an alternative to solid weld wires for improved productivity in structural fabrication. Metal-core weld wires are composite tubular filler metal electrodes having a metal sheath and a core containing a composition of various powdered materials. The core composition of metal-core wires includes iron powder, usually as filler material. The core composition comprises approximately 1 to 45% of the total wire weight. The iron powder content is usually considerable and comprises generally between approximately 0 and 44% of the total wire weight. During the manufacture of metal-core wires, the core composition is blended and deposited onto a steel strip, which is formed into a tube or sheath about the core composition in a forming mill. The steel sheath surrounding the core composition is then drawn through reducing dies to a specified diameter. Metal-core wires provide increased weld deposition rates and produce wider and more consistent penetration profiles than solid wires. In addition, metal-core wires generate less fumes and spatter, provide improved arc stability and produce weld deposits with improved wetting characteristic in comparison to solid wires. However, these productivity advantages which metal-core wires provide are sometimes offset by the time required to remove the slag deposits or islands which form on the surface of the weld.
Using conventional solid and metal-core wires, slag islands tend to form at the toe or edges of the weld. At this location, the weld has a somewhat concave contour as shown in FIG. 1. The slag deposit has a tendency to be drawn into this concavity making it very difficult to remove. In accordance with the present invention, it has been found that by making certain alloy additions to the solid and metal-core wire, the slag islands tend to form predominantly at a point that is removed from the edges of the weld. At these locations, the slag deposits either self-peel or they are easily removed.
U.S. Pat. No. 4,345,140 to Godai et al. is directed to a flux-cored composite wire for use in welding stainless steels. The patent discloses that the addition of low melting point metallic oxides such as lead, copper, bismuth, antimony and tin oxide is useful in enhancing the separability of slag. The low melting point metal oxide is preferably added in an amount of about 0.1 to 0.25%. A composite flux cored wire for stainless steel welding is fundamentally different than the mild steel and low alloy steel weld wires of the present invention. Flux cored wires for welding stainless steel contain a flux which includes nonmetallic inorganic components which, by comparison, are present in significantly higher percentages (e.g., 5 to 10%) than in a mild or low alloy metal core wire welding wires. A flux core wire produces a slag which covers the entire surface of the weld and adheres strongly to the weld bead making it very difficult to remove. Metal-core wires have a core composition comprising primarily metallic and alloying powders with substantially reduced amounts of nonmetallic components (e.g., less than 5%). In contrast to metal-core wires, flux core wires do not form small slag islands in the toe regions of the weld deposit.